The present invention relates to disk drive systems and, more particularly, to microactuator devices that function to provide fine movements of a transducing head so that densely spaced tracks on a disk may be accurately selected and followed to read and write more data on disk.
The present invention particularly pertains to a microactuator device for use in a multiple track disk drive system so that fine positioning of a transducing head over a selected track of the disk may be obtained, and more particularly, to a piezoelectric microactuator device that provides a simplified, low-cost construction when compared with the prior art designs.
Magnetic disk drives are information storage devices that use thin film magnetic media to store data. A typical disk drive as seen in FIG. 7 of U.S. Pat. No. 6,166,890, the disclosure of which is incorporated herein, includes one or more rotatable disks having concentric data tracks in which data is read or written. As a disk rotates, a head transducer, also referred to as a magnetic recording head, is supported by a slider and positioned by an actuator element to magnetically read data from, or write data to, various tracks on the disk. Typically, the head transducer is attached to a slider having an air-bearing surface, which is supported adjacent to a data surface comprising the data tracks by a film of air generated by the rotating disk. Suitable wires connect the transducer on the slider to a data processing unit that controls read/write electronic circuitry.
The radial spacing between data tracks continues to decrease with increase in recording density, requiring greater precision for head positioning. External and internal disturbances in a disk drive continuously move the head transducer off the data track. Conventional disk drives correct for off-track motion by actuating the arms carrying the head transducers using a voice coil motor. See the Figures of U.S. Pat. No. 6,115,223, the disclosure of which is incorporated herein by reference. However, a voice coil motor lacks fast response and sufficient resolution for small motions required to effectively maintain position of head on a track of a high-track density disk. Therefore, a secondary fast response high-resolution head positioning mechanism is necessary for small motions to reduce track registration error in high-density disk drives.
Some of the prior art piezoelectric microactuator designs correct for hard disk drive disk track misregistration. These include designs with piezoelectric microactuators mounted on arm, on suspension near hinge, or near or under the slider carrying the head transducer. Designs with piezoelectric microactuators mounted on the arm produce highest slider movement but excite undesirable voice coil motor coil, arm and suspension load beam modes. Designs with piezoelectric microactuators mounted near the hinge produce medium slider movement but excite undesirable arm tip and suspension modes. Designs with piezoelectric microactuators mounted near the slider produce small slider movement but excite minimum undesirable modes of flexure and load beam. Location of piezoelectric microactuators shall depend on a drive configuration and requirements.
The prior art Japanese patent 63-291271 has a piezoelectric element (formed by a U-shape through groove in a piezoelectric material plate) mounted under and concentric to the slider and appears only to provide translation motion along the long axis of the suspension more suitable for linear and not rotary actuators. Present invention differs in configuration of piezoelectric element, provides rotary motion in addition to the translation motion across the recorded data tracks, and is intended for use with rotary actuators.
U.S. Pat. No. 5,856,896 (xe2x80x9c""896 patentxe2x80x9d) teaches the use of two parallel piezoelectric elements on the leading edge of the slider attached to a suspension. It further teaches the use of a compliant shear layer connecting the slider and the suspension. The design of the xe2x80x9c896 patent has the disadvantage of using two piezoelectric elements instead of a single element. The design must also deal with fatigue problem related to the compliant layer. Japanese references JA 0097174 and JP 10-027446 also teach the use of two piezoelectric elements polarized in opposite direction and placed under the slider for angular motion. However, normal placement inaccuracies associated with the use of two piezoelectric pieces could result in asymmetrical loading, which in turn could result in undesirable dynamic modes. Also, accurate placement and bonding of two piezoelectric microactuators instead of one is more expensive. Present invention solves these problems by having a simple single element that is polarized in only one direction and placed accurately at slider center.
U.S. Pat. No. 6,166,890 discloses the mounting of the piezoelectric microactuators in the same plane and near the slider. The problem with this approach is that the design has a more complex mechanism like a cradle, is more fragile, excites more undesirable dynamic modes, and is more expensive to manufacture.
The present invention relates to piezoelectric microactuator locations under the slider and differs from others for having a simple low cost configuration, for providing a choice of rotary or translation motion of the slider based on attachment, and for moving transducer head across the tracks. The invention also offers alternate compact piezoelectric element with configurations that have large effective length for many times head movement to help in faster seek and settle. The invention also offers compact piezoelectric element configurations that produce many times larger force to overcome resistance of stiff suspension structures required by some applications.
The present invention involves an S-shaped piezoelectric element placed under the slider with leading leg bonded to the leading edge of the slider and trailing leg bonded to the flexure tongue. The leading and trailing legs of the S-shaped piezoelectric element are both polarized in the same direction. An application of electrical voltage to the top and bottom surfaces of the piezoelectric element results in a across the track translatory movement of the slider and head. Alternately, attachment of the center of the piezoelectric element to flexure and both ends to slider results in rotary movement of slider and head transducer across the track when voltage is applied. In addition, the S-shaped piezoelectric element can have more than three legs resulting in either increase in actuation force or increase in head movement based on configuration described above. The across-track motion due to the piezoelectric element is utilized by servo system to correct for off-track head motion caused by dynamic disturbances, thereby resulting in more accurate track following and recording of more data tracks on a disk for increased capacity and reduced seek time of a hard disk drive. The S-shape with three or more legs is formed by multiple recesses part of the way across the width from alternate sides into a flat piezoelectric material.
Briefly stated then, a fundamental provision of the present invention is defined as follows:
a disk drive system having an actuator arm to support a slider carrying a transducing head adjacent a selected data track of a rotatable disk having a plurality of concentric data tracks, the slider having an air-bearing surface generally parallel to and confronting the top surface of the rotatable disk, wherein a microactuator device effects fine positioning of the transducing head with respect to the selected data track, the microactuator device comprising the slider carrying a transducer head; a flexure, and an S-shaped piezoelectric element having opposite ends, wherein one end of the piezoelectric element is affixed or connected to one end of the slider, and the other end is affixed or connected to the flexure member for obtaining translation movement of the slider head transducer to enable tracking of the disk. Alternately, both ends of the piezoelectric element could be affixed to two ends of slider and center affixed to the flexure over dimple for pure rotary motion of the slider.
The foregoing and still further objects and advantages of the present invention will be more apparent from the following detailed explanation of the preferred embodiments of the invention in connection with the accompanying drawing.